powell



w. T. POWE'LL.

SELECTIVE SIGNALIHG SYSTEM. APPLICATION FILED pue.2a.191a.

1,306,716. Patented June 17, 1919.

3 SHEETS-SHEET 1.

W. T. POWELL.

SELECTIVE SIGNALING SYSTEM.

APPLICATION FILED AUG-23.1916.

Patentd June 17, 1919.

3 SHEETSSHEET 2- W. T. POWELL.

SELECTIVE SIGNALING SYSTEM.

APPLICATION FILED AUG.23,1916.

1 ,306,716. Patented June 1?, 1919.

3 SHEETS-SHEET 3.

JILL/N6 mum 57' E Nut/552 A as UNITED sTA'rEs PATENT OFFICE.

WINFRED T. POWELL, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRICCOMPANY, OF CHICAGO, ILLINOIS, CORPORATION OF ILLINOIS.

SELECTIVE SIGNALING SYSTEM.

Specification of Letters Patent. Patented June 17, 1919- Applicationfiled Aug 'ust 23, 1916. Serial No. 116,482.

tems which are provided with so-called r1ngback apparatus by means ofwhich a calling subscriber may signal a called subscriber on his ownline. In the patent to Hovland, #1,158,22l, there is described a systemof handling reverting calls in bridged automatic party line systems, inwhich the calling subscriber,'by' manipulating his dial in accordancewith the proper digits, operates a frequency selecting switch at theexchange, which switch selects simultaneously the two frequencies ofringing current which correspond to the calling and called substations.

' The calling subscriber then hangs up his receiver, whereupon mechanismin the frequency selector is put into operation to effect theapplication-of the two selected ringing currents to the calling linealternately. The called subscriber is thus signaled as usual; while thecalling subscriber is also signaled so that he may know that theoperation is proceeding in the proper manner, and also that he may beapprised of the response of the called subscriber by the cessation ofthe ringing operation which occursas soon as the called subscriberremoves his receiver. The calling subscriber will then remove hisreceiver also and converse as desired.

The Hovland system is adapted to handle calls from anyone of fourbridged substations to any one of the remaining three, there beingprovided the usual four frequencies of ringing current. The ob]ect ofthe present invention is to provide a revert- 1 ing call signalingsystem in which the usual four frequencies of ringing current are usedto selectively signal at the same time any two of eight substations onthe same llne, the ringers being connected four from one side of theline to ground and four from the other side of the line to ground.

Because of the fact that the ringers are not bridged across the line andbecause furthermore there are on each line two substations which respondto each frequency 01 phone line and the necessary central oflicecircuits and apparatus. Fig. 3 is a chart showing the telephone numberscorresponding to all possible two station combinations on an eight partyline.

Referring to Fig. 1 of the drawings, I have indicated by referencecharacters 11 and 12 a party line provided with eight substations whichare indicated by reference characters A. to A inclusive. Substation A,which is representive of the group, comprises essentially the receiver2, transmitter 3, switch hook 4, ringer 5, and condenser 6. Being anautomatic substation there is also provided a calling device comprisinga pair of impulse springs 7 and 8 controlled by the impulse cam 9through the medium of a finger hole dial (not shown). .A calling deviceof suitable design is shown and described in the British patent to S. G.S. Dicker, #29,654 of 1910. When the receiver is on the hook it will beseen that the ringer 5 is connected from the line conductor 12 toground. The substation A is similar to substation A but the ringer 5' isconnected from line conductor 11 to ground. In order to save space onlythe rin ers of the remaining six substations have een shown, three ofwhich are connected from line conductor 11 to ground and the other threefrom line conductor 12 to ground.

It has been found desirable in practice to use ringing currents offrequencies approximating 16, 33, 50, and 66 cycles per second. Inaccordance with this plan the ringers at substations A and A. areadapted to respond to the 16 cycle ringing current, the ringers atsubstations A and A to 33 cycle ringing current, the ringers atsubstations A and A. to 50 cycle ringing current, and

the ringers at substations Aand A to the 66 cycle ringing current.

At the exchange the line conductors 11 and 12 are terminated in anindividual line switch C, which is of the general type of line switchdisclosed in British patent to James #26301 of 1906; being, however,

more nearly of the particular type disclosed in U. S. Letters Patent#1,078,690, granted Jan. 17, 1912, to Frank Newforth. Since lineswitches of the foregoing type are well known in the art no extendeddescription will be given. It will suflice to say that through themedium of line switch C the party line shown is given access to aplurality of selector switches one of which 1s shown and is indicated byreference character E.

The line switch C, together with a plurality of similar line switches,is controlled in its selective operation by means of the master switchD, which is-of the general type of line switch disclosed in the abovementioned patent to James; being, however, more nearly of the particulartype disclosed in British patent to Martin, #1419 of 1910.

,The function of the master switch, as is well known, is to maintain theplungers of all the idle line switches which it controls in positionbefore the terminals of an idle trunk line.

The selector switch E is of the general type of selector switchdisclosed in U. S. Letters Patent #815,321, granted March 13, 1906, toKeith, Erickson, and Erlckson; being, however of the particular typedisclosed in the British patent to the Automatic Telephone Mfg. Co.,#2543 of 1914. A selector switch of the foregoing type is operable inresponse to the first digit of a called number to select one of aplurality of groups of trunk lines, after which the selector operatesautomatically to select an idle trunk line in the selected group and eX-tend connection thereto.

The selector switch E, in common with similar selectors, has accessthrough certain of its bank levels to other selectors (not shown) bymeans of which connections may be extended toward the lines of othersubscribers in the exchange, and it also has access through a separatebank level to a group of so-called frequency selectors, one of which isshown at F (Fig. 2).

The frequency selector F is a vertical and rotary directively controlledswitch and is similar in mechanical construction to the switch shown inU. S. Letters Patent #815,176, granted March 13, 1906, to Keith,Erickson, and'Erickson. The circuits are modified, however, to adapt theswitch to the two-wire system of control as shown in the Newforth U. S.Patent #13,901, reissued April 13, 1915, and are further modified toprovide for the more comprehensive ringing operations which have to beperformed. A still further modification lies in the provision of fourwipers instead of three and the omission of the upper or private bank.The wipers are mounted on the shaft in two sets which are spaced apart adistance equal to the space between five bank levels.

It follows that when the lower set of wipers is in engagement with a setof bank contacts in the first level the upper set of wipers will be inengagement with the corresponding set in the sixth level, and when thelower set of wipers is in engagement with a set of bank contacts in thesecond level the upper set of wipers will be in engagement with thecorresponding set in the seventh level, etc. From these considerationsit will be seen that the frequency selector bank is for practicalpurposes divided horizontally into two sections, that the switch shaftis operable for five vertical steps instead of ten, and that when theshaft is rotated corresponding contacts in the upper and lower halves ofthe bank will be selected simultaneously.

The lower five levels of the frequency selector bank have certain oftheir contacts connected in suitable manner to the four ringing currentgenerators R, R R and R, whereby selection of the proper ringingcurrents may be accomplished through the medium of the wipers 123 and124. The three interrupters I, I and 1 which are mounted on a commonshaft, are suitably connected to the proper bank contacts in the upperfive levels, thereby providing means for controlling via the wipers 121and 122 the application of the selected ringing current, or currents, tothe calling line.

The necessity for the simultaneous selection of ringing currents andcontrolling circuits therefor may be seen from a more detailedconsideration of the functions the frequency selector has to perform. Inbroad language the frequency selector must be provided with meanswhereby any one of the eight subscribers on a calling line, the line1112 for example, may ring his own bell and the bell of any othersubscriber on the same line alternately. Because of the arrangement ofthe substation ringers, two to each ringing current frequency connectedon opposite sides'of the line to ground, there arises four differentconditions under which thesignaling must be accomplished. The chart Fig.3 shows every possible combination with the necessary telephone numbersand these different combinations are arranged in four groups accordin tothe signaling operation required. Brie y stated, the first groupincludes all calls in which only one ringing current generator is'selected and which is applied to, the two sides of the calling linealternately; the second group includes all calls in which two generatorsare selected and applied alternately to one side of the calling line;the third group is similar to group twoexcept that it relates to theother side of the calling line; while the fourth group includes allcalls in which two generators are selected and applied alternately oneto one side of the calling line and the means other to the other side.Means are provided in the frequency selector F for reversing theincoming line and for switching from one selected generator to theother, which means comprise the relays 114 and 115. These relaystogether with a ringing relay 113 are controlled by the three ringinginterrupters II inclusive, to produce the desired results, all in amanner which will be fully explained hereinafter. For the purposes ofthis explanation, it will first be assumed that the subscriber atsubstation A desires to signal the subscriber at substation A this beingthe connection illustrated in the drawings. Afterward connectionsrepresentative of the other ringing conditions will be brieflydescribed. Inasmuch as a large portion of the automatic equipment usedis old and well known in the art, having been fully described in thepublications referred to, the operation will be described in a more orless general manner except where it has to do with the principles of theinvention.

When the calling subscriber at substation A removes his receiver toinitiate the call, an energizing circuit is completed over the lineconductors 11 and 12 for the line relay 14 of the line switch C. Uponattracting its armature, the line relay 14 closes a, circuit for thepull-in winding 18. Upon energizing, the pull-in winding operates boththe plunger arm 15 and the cut-off armature 16; the former through themedium of its plunge (not shown) forcing the bank springs 3033,'inclusive, into engagement, respectively, with contacts 3437, inclusive;and the latter disconnecting the line conductors 11 and 12,respectively, from ground and from the line relay 14. By the engagementof bank springs 30 and 33 with contacts 34 and 37, respectively, theline conductors 12 and 11 are extended through normally closed contactsof the switching relay 63 to the double-wound line relay 50 of theselector E.

The line relay 50 is accordingly energized over the loop circuitincluding substation A and, upon attracting its armature, closes acircuit for the slow-acting release relay 51. Upon energizing, therelease relay closes a holding circuit for the line switch C which maybetraced from ground G by Way of contact springs 65, contact 35, bankspring a 31 and the holding winding 17 to battery B. Since the linerelay 14 is slow-acting, it retains its armature to maintain. thepull-in winding 18 energized until after the above holding circuit has.been established. A

branch of the holding circuit extends by way of conductor 20 to multipletest contacts in the banks of connector switches having access to theline of substation A where by a ground potential on these test contactsthe said line is made busy. By the engagement of bank spring 32 withcontact 36 a circuit is closed whereby the master switch D is opnowmanipulate his dial in accordance with the first digit 0 of the desirednumber, thereby separatmg momentarily the impulse springs 7 and 8 tentimes and interrupting each time the circuit of line relay 50 ofselector E. As a result of these interruptions of its circuit the linerelay 50 is deenergized a corresponding number of times, sending animpulse at each deenergization from ground at Gr to the slow-actingrelay 62 and the vertical magnet 65 in series. The verticalmagnet, inresponse to these impulses, steps up the switch shaft until the wipers70, 71, and 72 stand opposite the horizontal level in which are locatedcontacts which are terminals of the group of frequency selectors Therelay 62, being slow-acting, retains its armature during the series ofimpulses and closes a circuit for the test relay 64, which latter relayprepares a circuit for the rotary magnet 66 and locks itself to groundat G At the end of the series of impulses the relay 62 deenergizes,thereby completing the aforementioned circuit of the rotary magnet 66,whereupon the wipers 70, 71, and 72 start rotating in search of an idletrunk line. As is well known, the rotary magnet interrupts its owncircuit and also the locking circuit of the test relay at everyenergization, the contacts in the latter circuit, however, beingshort-circuited by the test or private wiper 71 while passing overgrounded busy contacts. As soon, therefore, as the test wiper 71 arrivesat an under-. ground test contact the test relay 64 deenergizes andopens the rotary magnet circuit, thereby bringing the wipers to restupon the terminals of an idle trunk line, assumed to be in this case thecontacts 73, 74, and 75. As a further result of the. deenergization ofthe test relay 64, a circuit is completed for the line switching relay63 which relay, upon energizing, disconnects the extended lineconductors 12 and 11 from the windings of the line relay 50 and furtherextends them by way of wipers and 72, bank contacts 73 and 75, and trunkline con-- ductors 180 and 181 to the double-wound line relay 100 of thefrequency selector F.

The line relay 100 thereupon energizes over the line circuit extendingback through substation A and completes an energizing circuit for theslow-acting relay'101. Re-

lay 101, upon attracting its armature, prepares a circuit for thevertical and rotary magnets 104 and 105 and also completes a new holdingcircuit as follows: ground at G, contact springs 119, bank contact 74and wiper 71 to wire junction 80, where the circuit divides, one branchextending by way of a back contact of relay 64 through the winding ofline switching relay 63 to battery 13, and the other branch extending byway of off-normal contact 67 and interrupter contact 81 to wire junction82 where it joins the previously described holding circuit extendingback to the line switch C.

The subscriber at substation A may now operate his dial in accordancewith the second digit 2 of the desired number, resulting now indeenergizations of the line relay 100 of the frequency selector F. Ateach dccncrgization the line relay 100 sends an impulse from ground at Gto the slow-acting relay 107 and the vertical magnet 104 in series, sideswitch wiper 115 being in its first position. The vertical magnet, inresponse to these impulses, steps up the shaft until the upper and lowersets ofwipers stand opposite, respectively, the seventh and the secondhorizontal levels of bank contacts. Relay 107, being slow-acting,retains its armature during the series of impulses and maintains acircuit from ground at G for the private magnet 108. At the end of theseries of impulses, the relay 107 denergizes and breaks the circuit ofthe private magnet, which latter controls the side switch wiper 115 inthe usual manner to advance it to its second position.

The subscriber at substation A may now operate his dial in accordancewith the third and final digit 1 of the desired number, resulting now inasingle deenergization of the line relay 100. Side switch wiper 115being in its second position, the line relay in response thereto sendsan impulse to the slowacting relay 107 in series with the rotary magnet105. The rotary magnet operates in response to this impulse to rotatethe upper wipers 121 and 122 and the lower wipers 123 and 124 until theyengage the f rst sets of bank contacts in the respective levels to whichthey have been raised. The relay 107 and the private magnet 108 areenergized during the last series of impulses as before, the latter upondeenergizing, again controlling the side switch wiper 115 to advance itto its third position.

The foregoing operations of the frequency selector are practicallyidentical with the operation of the connector described in the abovementioned Newforth patent. The remaining operations will be describedwith considerable more detail. Having opera-ted his calling device toperform the necessary selective operations at the exchange, the callingsubscriber at substation A will now hang up his receiver, thereby againbreaking the circuit of the line relay 100. Upon deenergizing, the linerelay completes a circuit for the switching relay 112 over the followingpath: ground at G, closed contacts of line relay 100, contact springs120, winding of relay 107, contact springs 131, winding of relay 112,and side switch wiper 115 (in third position) to battery B. Relay 107 isnot energized. Relay 112, upon attracting its armature, first completesa circuit by which the slow-acting release relay 101 may be keptenergized independent of the -line relay 100 and which may be traced asfollows: ground at G, contact springs 132, and winding of relay 101 tobattery B. As a further result of the energization of relay 112 theincoming trunk line conductors 180 and 181 are disconnected from thewindings of the line relay 100 at contact springs 146 and 149,respectively, and are connected instead by way of contact springs 144and 147 to the contact springs 135 and 138 of the ringing relay 113.Finally, assuming that the interrupter I is in the position shown, acircuit is completed for the ringing relay 113 as follows: ground at G,interrupter I, conductor 150, contact springs 1.33, and winding of relay113 to battery B.

Upon the energization of the ringing relay 113, a circuit for thegenerator R is com pleted as follows: ground at G", generator R, uppercontact 2 up and 1 in, wiper 123, contact springs 161 and 162, contactsprings 166 and 165, contact springs 137 and 138, contact springs 147and 148, trunk line conductor 181 to bank contact 75, thence by Way ofwiper 72, contact springs of switching relay 63,bank contact 37, spring33, line conductor 11, and ringers of substation A A A and A in parallelto ground, and thence back to ground G", the starting point. Upon theclosure of the above circuit, the ringer at substation A which is theringer corresponding to the frequency of generator R, responds tothereby notify the subscriber that he is wanted. After a brief intervalthe ringing relay circuit is broken by the rotation of the interrupter Iand the said ringing relay deenergizes. It will be observed that theinterrupter I has two live segments, providing for two ringing periodsat each complete revolution, while the interrupters l and I have but onelive segment each. It follows, therefore, that in the second half of therevolution of the interrupter shaft the circuit of the ringing relay 113will again be completed. Also at the same time or an instant before thefollowing circuit is completed by interrupter I ground at G, interrupterI conductor 152, upper bank contact 7 up and 1 in, wiper 121, contactsprings 171 and 170, and winding of relay 114 to battery B. As has beenpreviously mentioned the relay 114 is a reversing relay which now, uponenergizing, operates to complete the circuit of generator R over thetrunk line conductor 180 instead of the conductor 181. Beginning atcontact spring 162 of relay 115 the generator circuit extends asfollows: contact spring 162, contact springs 167 and 168, contactsprings 134 and 135, contact springs 144 and 145, trunk line conductor180 to bank contact 73, thence by way of wiper 70, contacts of theswitching relay 63, bank contact 34, spring 30, line conductor 12, andthe ringers at substations A, A A and A in parallel to ground. Theringer at substation A now responds, thereby notifying the callingsubscriber that the operation is proceeding satisfactorily.

The operation continues as described until either the calling or calledsubscriber res moves his receiver, the ringing relay 113 being energizedtwice at every revolution of the interrupter shaft while the reversingrelay 114 is energized at every other energization of the ringing relay,thereby ringing the bells at substations A and A alternately.

When the called subscriber at substation A removes his receiver toanswer the call, a circuit for the ring cut-0E relay 106 is completedwhich, in case ringing relay 113 is not energized, extends as follows:ground at G, contact springs 139 and 138, and contact springs 147 and148 to trunk line conductor 181, thence over previously traced path toline conductor 11, thence by way of the receiver and transmitter ofsubstation A to line conductor 12, thence over previously traced circuitto trunk line conductor 180, thence by way of contact springs 145 and1%, contact springs 135 and 136, and winding 109 of relay 106 to batteryB. In case the ringing relay is energized the trunk line conductor 181will be grounded at G" via the previously traced circuit of generator RHence,in this instance, ground at G" will be substituted for ground (3in the above traced circuit, and in addition the battery end of thecircuit, instead of passing direct from contact springs 135 and 136- ofthe ringing relay to the winding 109, will extend as follows: contactsprings 135 and 134, contact springs 168 and 169, and winding 109 ofrelay 106 to battery B. In case the reversing relay 114 is energized thecircuit for the ring cut-off relay 106 will be the same as in thecondition just/mentioned except that the trunk line conductors 180 and181 are reversed as regards their connection to ground and battery,respectively.

In any case, it will be seen that when the receiver is removed atsubstation A, a circuit will be completed for the ring cut-off relay106. Upon attracting its armature, relay 106 looks itself over thefollowing circuit: ground at G, ofi-normal contact 140, contact springs142, and winding 110 to battery 13. At the same time a circuit for theprivate magnet 108 is closed as follows: ground G ofl"-nor1nal contact140, contact springs 141, and winding of private magnet 108 to batteryB. The private magnet, upon energizing, disconnects the wipers 121 and122, respectively, from relays 114 and 115. As a further result of theenergization of the ring cut-ofi' relay 106 the circuit of the switchingrelay 112 is broken at contact springs 131. Upon denergizing, theswitching relay 112 restores the original circuit by which the trunkline conductors 180 and 181 are again extended to the double-wound linerelay 100. The line relay 100 accordingly energizes as before, exceptthat the loop includes substation A instead of substation A, and uponattracting its armature, again completes the circuit of the slow-actingrelease relay 101 over the original path.

The ringing operation has now been stopped. Being apprised thereby ofthe fact that the wanted subscriber has ansnered," the subscriber atsubstation A will now remove his receiver also, and is then able toconverse with the subscriber at substation A as desired. Current issupplied to the two transmitters in parallel from the windings of theline relay 100, while the voice currents take the path shown in.

heavy lines.

When the conversation is finished both subscribers will hang up theirreceivers. When the last receiver is replaced the circuit of the linerelay 100 is broken, which relay therefore deenergizes to break thecircuit of the slow-acting release relay 101. Upon deenergizing, therelease relay 101 closes a circuit for the release magnet 111 in theusual manner, whereupon the frequency selector F is restored to normaltherefore that the selector E and the line switch C are restored tonormal position in the usual and well known manner, whereare broughtinto engagement with the fifth set of contacts in the fourth level andthe nected to'the generator R, whichis the generator to which the ringerat substation A responds; while the upper bank contact 4 up and 5 in isconnected to the generator R which is the generator to which the ringerat substation A corresponds. It will be observed, further, that thelower bank contact 9 up and 5 in, with whichthe wiper 122 is inengagement, is connected to conductor 152 extending to interrupter 1 Andlastly it will be seen that since relay 114 is deenergized the middlespring 162 of relay 115 is connected via a path previously traced to theline conductor 11 from which the ringers at substations A and A areconnected to ground. Now it will be clear that as the interrupter shaftrevolves the ringer relay 113 will be energized twice for eachrevolution of the interrupter. I while the relay 115 will be energizedat every other energization of the ringing relay or once per revolutionof interrupter I As a result first generator R and then generator R isconnected to line conductor 11 whereby the two substations are signaledalternately.

Assuming now that substation A is calling substation A in which case theupper and lower sets of wipers will have been advanced, respectively, tothe third contact set in the ninth level and the third contact set inthe fourth level, the operations are the same as in the last case, withthe addition that the reversing relay 114 must now be operated at eachenergization of the ringing relay 113, for the ringers at thesesubstations are connected from line conductor 12 to ground. Aninspection of the bank wiring will now show that a conductor 151, abranch of conductor 150, extends from interrupter I to the upper contactof the set 9 up and 3 in, which in the case of contact set 9 up and 5 inwas vacant. Now as the mterrupters revolve, the relays 113 and 114 areenergized simultaneously twice at each revolution of interrupter I whilerelay 115 is energized once per revolution as before. This operationresults in the alternate connection of generators R and R to the lineconductor 12 whereby the substations A and A are signaled alternately.

One more casewill be considered-the case where the subscriber atsubstation A is callin the subscriber at substation A. The te ephonenumber to be called is 022, resultmg in the selection of the second setsof contacts in the second and seventh levels. From an inspection of thebank wiring it will be seen that the upper and lower contacts of thesecond set in the second level are connected, respectively, togenerators R and R It will be seen, furthermore, that the upper andlower contacts of the second contact set of the seventh level areconnected, respectively, to the interrupters. 1 and I. Also it should benoted that the live segments of the interrupters I and I arestaggeredwith respect to each other. It follows therefore that in acertain part of the revolution of the interrupters the relays 113 andlltwill be energized simultaneously, followed later by the simultaneousenergization of relays 113 and 115. In the first case generator R willbe connected to line conductor 12 to operate the signal at substation Awhile in the latter case generator R will be connected to line conductor11 to operate the signal at substation A Since all the remainingcombinations shown on the chart fall within one or the other of thecases already described, it is thought that the circuits can be tracedreadily enough without further explanation.

While I have shown the circuits in the preferred form, they aresusceptible to modifications to provide for other conditions. Inaddition it is to be noted that the wiring of the frequency selectorbank as shown is largely an arbitrary arrangement. Care has been taken,however, to prevent the crossing together of generators by so arrangingthe bank wiring that whenever two adjacent contacts are in use they areboth connected to the. same generator.

Having fully described and illustrated my invention, what I consider tobe new and desi re to have protected by Letters Patent will be pointedout in the appended claims.

\Vhat I claim as my invention is:

1. In a telephone system, a party line provided with substation ringersconnected from opposite sides of said line to ground, a calling terminaland a called terminal for said line, ring-back apparatus at theexchange. mcans for extending a connection from said line to said ringback apparatus via said calling terminal, and means for operatin saidapparatus to project ringing current ack over said calling terminal tothe calling line to enable one party to selectively signal the otherparties on the same line.

2. In a telephone system, the combination with a party line providedwith substation ringers connected from opposite sides of said line toground, of a plurality-of grounded ringing current generators at theexchange, and automatic means controlled over said line for connectingeither conductor thereof to the ungrounded pole of any generator.

3. In a telephone system, a party line,

lea

substation ringers connected from opposite sides of said line to round,and a ring-back apparatus for enabling one party on said line to *allanother on the same line. said ring-back apparatus comprising means fortransmitting ringing current first over one side of said line and thenover the other.

4. In a telephone system, a party line, sub station ringers connectedfrom one side of said line to ground, and a ring-back apparatus forenabling one party to call another on the same line, said apparatuscomprising means for transmitting in alternation two different kinds ofringing current. over the ringer side of said line.

In a telephone system, a party line, substation ringers connccted fromopposite sides of said line to ground, a plurality of grounded ringingcurrent generators for supplying ringing currents of differentcharacter, and subscriber controlled means for selecting and connectingany one of said generators to either side of said line.

6. In a telephone system, a party line, a calling terminal for said lineand a called terminal for said line, a ring-back apparatus for enablingone party to call another on the same line, means for extending aconnection from said line to said ring back apparatus, said apparatuscomprising means for signaling the stations on said line by projectingringing current back over said calling terminal and over one side ofsaid line and ground, and also comprising means operated over the twosides of said line in series for stopping the signaling operation.

7. In a telephone system, a line, an automatic switch, a plurality ofgenerators, means for operating said switch over said line to select twoof said generators, a conductor means for connecting said conductor toeither selected generator sepa-' rately, and means for connecting saidconductor to either side of said line separately.

8. In a telephone system, a line, an automatic switch, a plurality ofgenerators, means for operating said switchover said line to select anyone of said generators, and means for connecting the selected generatorto either side of said line separately.

9. In a telephone system, a line, an automatic switch, a plurality ofgenerators, means for operating said switch over said line to select anytwo of said generators, and means for connecting the said enerators inalternation toone conductor ot said line to the exclusion of the otherconductor.

10. In a telephone system, a subscribers line, a plurality of ringinggenerators for supplying ringing currents of difi'erent character, andmeans including a switching device controlled over said line whereby asubscriber thereon may select at his option any one of said generatorsseparately or any two of said generators simultaneously.

lluIn a telephone system, a subscribers metallic line circuit,substation ringers connected from each side of said circuit to ground, aplurality of grounded ringing current generators for supplying ringingcurrents of diiferent character, an automatic switching device forselecting any one of said generators. and means for connecting theungrounded pole of the selected generator to the two sides of said linecircuit alternately. I

12. In a telephone system, a party line, substation ringers connectedfrom each limb of said line to ground, a plurality of grounded ringingcurrent generators for supplying ringing currents of ditterentcharacter, an automatic switching device for selecting any two of saidgenerators, and means for connecting the ungrounded poles of saidgenerators alternately to one limb of said line.

13. In a telephone system, a party line, substation ringers connectedfrom each limb of said line to ground, a plurality of grounded ringingcurrent generators for supplying ringing currents of differentcharacter, an automatic switching device for selecting any two of saidgenerators, and meansfor connecting in alternation the ungrounded poleof one selected generator to one limb of said line and the ungroundedpole of the other selected generator to the other limb of said line. a

14-. In a telephone system, a party line, a plurality of ringing currentgenerators for selective signaling on said line. a plurality ofinterrupters for controlling the signaling operation. and an automaticswitching device controlled over said line for simultaneously selectingone of said generators and one of said interrupters.

15. In a telephone system, a party line. a plurality of ringing currentgenerators for selective signaling on said line, a plurality ofinterrupters for controlling the signaling operation, and an automaticswitching device contiolled over said line for simultaneously selectingany two of said generators and one of said interrupters.

16. In a telephone system, a party line, a plurality of ringing currentgenerators for selective signaling on said line. a plurality ofinterrupters for controlling the signaling operation, and an automaticswitching device controlled over said line for simultaneously selectingtwo of said generators and two of said interrupters.

17. In a telephone system, party lines, a plurality of ringing currentgenerators for selective signaling on said lines, controlling circuitsof difi'ercnt character for cont rolling the signaling operations, andsubscriber controlled means for simultaneously selecting one of saidgenerators and one of said controlling circuits.

18. In a telephone system, a party line,-

substation signals connected in different relation to said line, ringingcurrent generators and mechanism for connecting the same to said line,controlling circuits of difi'erent character corresponding to thedifferent arrangements of said signals for controlling said mechanism,and subscriber controlled means for selecting the proper controllingcircuit.

19. In a telephone system, a line, a plurality of ringing currentgenerators, an automatic switching device controlled over said lineforselecting one of said generators and for connecting one conductor ofsaid line thereto, a relay for controlling said connection connected tothe other conductor of said line, and a second relay for reversing thesaid line conductors as regards their connection, respectively, to theselected generator and the said first relay.

20. In a telephone system, a party line, substation ringers connectedfrom opposite sides of said line to ground, anda ring-back apparatus forenabling one party on said line to call another on the same line, saidring-back apparatus comprising two or more relays for causing ringingcurrent to be transmitted first over one side of said line and then overthe other.

21. In a telephone system, a party line, substation ringers connectedfrom one side of said line to ground, and a ring-back apparatus forenabling one party to call another on thesame line, said apparatuscomprising a plurality of relays for controlling the application of twodifierent kinds of ringing current to the ringer side of said linealternately.

22. In a telephone system, a line, an automatic switch, a plurality ofgenerators, means for operating said switch over said line to select twoof said generators, a con ductor, a relay for connecting said conductorto either selected enerator separately, and another relay for connectingsaid conductor to either side of said line separately.

23. In a telephone system, a line, an automatic switch, a plurality ofgenerators, means for operating said switch over said line to select anyone of said generators, and means for connecting the selected generatorto either side of said line separately while said switch remains in anoperated condition.

- 24. In a telephone system, a line, an automatic switch, a plurality ofgenerators, means for operating said switch over said line to select anyone of said generators, and for connecting the selected generator toeither side of said line separately.

25. In a telephone system, a line, an automatic switch, a plurality ofgenerators, means for operating said switch over said line to select anytwo of said generators, and means comprising two or more relays forconnecting the said generators in alternation to one conductor of saidline to the exclusion.

' of the other conductor.

26. In a telephone system, a subscribers metallic line circuit,substation ringers con nected from each side of said circuit to ground,a plurality of grounded ringing current generators for supplying ringingcurrents of different character, an automatic switching device forselecting any one of said generators, and electromagnetic means forconnecting the ungrounded pole of the selected generator to the twosides of said line circuit alternately.

27 In a telephone system, a party line, substation ringers connectedfrom each limb of said line to ground, a plurality of grounded ringingcurrent generators for supplying ringing currents of diiferentcharacter, an automatic switching device for selecting any two of saidgenerators. and electromagnetic means for connecting the ungroundedpoles of said generators alternately to one limb of said line.

28. In a telephone system, a party line, substation ringers connectedfrom each limb ofsaid line to ground, a plurality of ground ed ringingcurrent generators for supplying ringing currents of differentcharacter, an automatic switching device for selecting any two of saidgenerators, and automatic means for connecting in alternation the'unground ed pole of one selected generator to one limb of said line andthe ungrounded pole of the other selected generator to the other limb ofsaid line. I

Signed by me at Chicago, Cook county, State of Illinois, this 31st dayof July, 1916.

WINFRED T. POWELL.

